In the past, a large number of pharmacologists and chemists made efforts to chemically alter and/or modify the in vivo activity of naturally existing, physiologically active molecules. These efforts mainly focused on increasing or prolonging certain in vivo activity, reducing toxicity, eliminating or reducing side effects, or modifying specific physiological activities of the physiologically active substances. When a physiologically active substance is chemically modified, it loses some or most of its physiological activities in many cases. However, in some cases, the modification could result in an increase or change in physiological activity. In this regard, many studies have been focused on chemical modification capable of achieving desired physiological activity, and most of such studies have involved covalently bonding a physiologically active substance (drug) to a physiologically acceptable carrier.
For example, International Pat. Publication No. WO 01/93911 employs a polymer having a plurality of acid moieties as a drug carrier. International Pat. Publication No. WO 03/00778, discloses an anionic group-containing amphiphilic block copolymers that, when used as a drug carrier for a cationic drug, improve the stability of the drug. European Pat. No. 0 681 481 describes a method of improving the properties of basic drugs by using cyclodextrin and acids as carriers. On the other hand, hydrophobic drugs have low stability in vivo mainly due to their low aqueous solubility. To improve the low aqueous solubility of hydrophobic drugs, International Pat. Publication No. WO 04/064731 employs a lipid as a carrier. However, to date, there is no report for the use of an immunoglobulin Fc fragment as a drug carrier.
Typically, since polypeptides are relatively easily denatured due to their low stability, degraded by proteolytic enzymes in the blood and easily eliminated through the kidney or liver, protein medicaments, including polypeptides as pharmaceutically effective components, need to be frequently administered to patients to maintain desired blood level concentrations and titers. However, this frequent administration of protein medicaments, especially through injection causes pain for patients. To solve these problems, many efforts have been made to improve the serum stability of protein drugs and maintain the drugs in the blood at high levels for a prolonged period of time, and thus maximize the pharmaceutical efficacy of the drugs. Pharmaceutical compositions with sustained activity, therefore, need to increase the stability of protein drugs and maintain the titers at sufficiently high levels without causing immune responses in patients.
To stabilize proteins and prevent enzymatic degradation and clearance by the kidneys, a polymer having high solubility, such as polyethylene glycol (hereinafter, referred to simply as “PEG”), was conventionally used to chemically modify the surface of a protein drug. By binding to specific or various regions of a target protein, PEG stabilizes the protein and prevents hydrolysis, without causing serious side effects (Sada et al., J. Fermentation Bioengineering 71: 137-139, 1991). However, despite its capability to enhance protein stability, this PEG coupling has problems such as greatly reducing the number titers of physiologically “active” proteins. Further the yield decreases with the increasing molecular weight of PEG due to the reduced reactivity with the proteins.
Recently, polymer-protein drug conjugates have been suggested. For example, as described in U.S. Pat. No. 5,738,846, a conjugate can be prepared by linking an identical protein drug to both ends of PEG to improve the activity of the protein drug. Also, as described in International Pat. Publication No. WO 92/16221, two different protein drugs can be linked to both ends of PEG to provide a conjugate having two different activities. The above methods, however, were not very successful in sustaining the activity of protein drugs.
On the other hand, Kinstler et al. reported that a fusion protein prepared by coupling granulocyte-colony stimulating factor (G-CSF) to human albumin showed improved stability (Kinstler et al., Pharmaceutical Research 12(12): 1883-1888, 1995). In this publication, however, since the modified drug, having a G-CSF-PEG-albumin structure, only showed an approximately four-fold increase in residence time in the body and a slight increase in serum half-life compared to the single administration of the native G-CSF, it has not been industrialized as an effective long-acting formulation for protein drugs.
An alternative method for improving the in vivo stability of physiologically active proteins is by linking a gene of physiologically active protein to a gene encoding a protein having high serum stability by genetic recombination technology and culturing the cells transfected with the recombinant gene to produce a fusion protein. For example, a fusion protein can be prepared by conjugating albumin, a protein known to be the most effective in enhancing protein stability, or its fragment to a physiologically active protein of interest by genetic recombination (International Pat. Publication Nos. WO 93/15199 and WO 93/15200, European Pat. Publication No. 413,622). A fusion protein of interferon-alpha and albumin, developed by the Human Genome Science Company and marketed under the trade name of ‘Albuferon™’, increased the half-life from 5 hours to 93 hours in monkeys, but it was known to be problematic because it decreased the in vivo activity to less than 5% of unmodified interferon-alpha (Osborn et al., J. Phar. Exp; Ther. 303(2): 540-548, 2002).
Recombinant DNA technologies were applied to fuse a protein drug to an immunoglobulin Fc fragment. For example, interferon (Korean Pat. Laid-open Publication No. 2003-9464), and interleukin-4 receptor, interleukin-7 receptor or erythropoietin (EPO) receptor (Korean Pat. Registration No. 249572) were previously expressed in mammals in a form fused to an immunoglobulin Fc fragment. International Pat. Publication No. WO 01/03737 describes a fusion protein comprising a cytokine or growth factor linked to an immunoglobulin Fc fragment through peptide linkage. In addition, U.S. Pat No. 5,116,964 discloses proteins fused to the amino- or carboxyl-terminal end of an immunoglobulin Fc fragment by genetic recombination. U.S. Pat. No. 5,349,053 discloses a fusion protein comprising IL-2 fused to an immunoglobulin Fc fragment through peptide linkage. Other examples of Fc fusion proteins prepared by genetic recombination include a fusion protein of interferon-beta or its derivative and an immunoglobulin Fc fragment (International Pat. Publication NO. WO 00/23472), and a fusion protein of IL-5 receptor and an immunoglobulin Fc fragment (U.S. Pat. No. 5,712,121), a fusion protein of interferon alpha and the Fc fragment of immunoglobulin G4 (U.S. Pat. No. 5,723,125); and a fusion protein of CD4 protein and the Fc fragment of immunoglobulin G2 (U.S. Pat. No. 6,451,313).
Techniques involving the modification of amino acid residues of an immunoglobulin Fc fragment are also known. For example, U.S. Pat. No. 5,605,690 discloses a TNFR-IgG1 Fc fusion protein, which is prepared by genetic recombination using an IgG1 Fc fragment having amino acid alterations in the complement binding region or receptor binding region. Also, other methods of preparing a fusion protein using a modified immunoglobulin Fc fragment by genetic recombination are disclosed in U.S. Pat. Nos. 6,277,375, 6,410,008 and 6,444,792.
Such Fc fusion proteins produced by genetic recombination have the following disadvantages: protein fusion occurs only in a specific region of an immunoglobulin Fc fragment, which is at an amino- or carboxyl-terminal end; only homodimeric forms and not monomeric forms are produced; and a fusion could take place only between the glycosylated proteins or between the aglycosylated proteins, and it is impossible to make a fusion protein composed of a glycosylated protein and an aglycosylated protein. Further, a new amino acid sequence created by the fusion may trigger immune responses, and a linker region may become susceptible to proteolytic degradation.
To solve these problems, the inventors of the present application conducted a research, and came to a knowledge that, when a drug is administered in the form of being linked to an IgG Fc fragment, the drug has improved in vivo stability while exhibiting a minimal reduction in the in vivo activity.